Usually, optical fibres are fed from feed spools to be laid in the helical grooves of a carrier core which is then driven in translation, said feed spools being mounted on a plate or support rotating at a rate of one turn per pitch length advance of the carrier core and its grooves. Consequently, the spool plate or support rotation speed must be permanently synchronized with the apparent rotation of the helical grooves about the axis of the core during its translation movement so that the spools feed the fibres at a correct angle and are consequently well positioned in the grooves.
In accordance with a previously made suggestion, a die bearing a stud which engages a helical groove in the core has the function of allowing electric detection of the apparent rotation speed of the helical grooves during the translation movement of the core. In the corresponding fibre laying unit for laying fibres on the grooved core, said stud is a relatively fragile component and further, it causes or may cause wear and hence damage to the profiles of the grooves and is itself subject to very rapid wear.
The present invention aims to remedy such drawbacks by producing a simple but very strong apparatus for tracking the paths of helical grooves in the periphery of a core whose groove paths the apparatus follows when the core is moved in translation.